These days, in a motor vehicle, it is known practice to mount, in each wheel, an electronic measurement module comprising one or more sensors in order to detect a wheel anomaly. These sensors can for example be a sensor of the inflation pressure of the tire and/or a wheel acceleration sensor.
FIG. 1 schematically shows a motor vehicle 1A comprising an electronic control unit 5A and ten wheels 10A (numbered from 10A-1 to 10A-10) each comprising an electronic measurement module 100A (numbered from 100A-1 to 100A-10).
Each module 100A sends its measurements to the electronic control unit 5A which uses them to detect an anomaly and inform the driver thereof. To this end, each electronic measurement module 100A emits, to the electronic control unit 5A, over a radio communication link L0, signals in which messages comprising the measurements are coded.
In the existing solutions, each module 100A emits the signals over a same type of radio communication link L0 independently of the other modules 100A.
Such operation requires each module 100A to emit the same message several times with a high power to ensure that the electronic control unit 5A receives a given message at least once, and all the more so since the module 100A is mounted in a wheel 10A that is far away, in terms of power, from the electronic control unit 5A, which is energy-intensive (that is to say degrades the energy budget) for each module 100A.
Such a method for uploading measurements from the modules 100A to the electronic control unit 5A is not efficient and significantly reduces the battery life of the modules 100A, which necessitates excessively frequent maintenance and therefore presents a major drawback.
One obvious solution would consist in using a plurality of electronic control units 5A distributed in the vehicle 1A, but that would significantly increase the cost and the complexity of the vehicle and would therefore present a significant drawback.
The aim of the invention is to at least partly remedy these drawbacks by proposing a simple, reliable and efficient solution, for communicating measurements and information between the modules and the electronic control unit which is energy-efficient and inexpensive.
To this end, the first subject of the invention is a method for communicating measurement messages between a plurality of electronic measurement modules and an electronic control unit of a motor vehicle, each of the electronic measurement modules being mounted in a wheel of said vehicle, said method comprising the steps of:                measurement, by at least one first electronic measurement module called primary emitter module, of parameter values associated with the wheel in which said primary emitter module is mounted,        sending, by said primary emitter module, over a first radio communication link at a power below a first threshold, of measurement messages to at least one second electronic measurement module called relay module,        reception, by said relay module, of the measurement messages sent over the first radio communication link,        measurement, by the relay module, of parameter values associated with the wheel in which said relay module is mounted,        sending, by the relay module, of the measurement messages received and of its own measurements to the electronic control unit over a second radio communication link at a power above a second threshold, higher than or equal to the first threshold.        
The expression “sending messages” should be understood to mean the emission of radio signals in which are coded messages comprising measurements performed by an electronic measurement module or any other information, such as the identifier of the electronic measurement module for example.
The method according to the invention allows the electronic measurement modules furthest away from the electronic control unit in terms of radio power (that is to say the primary emitter modules) to emit measurement messages at low power to an electronic measurement module closer to the electronic control unit in terms of radio power (relay module) which then acts as a relay to transmit the measurements to the electronic control unit. Thus, with the method according to the invention, it is no longer necessary for the electronic measurement modules furthest away in terms of radio power to emit one and the same measurement message several times in succession, or to transmit at a high power since the message will be relayed by a relay module, closer to the electronic control unit, which makes it possible to save the energy of the primary emitter modules. The method according to the invention thus makes it possible to optimize the management of the electrical energy power supply batteries of at least some of the electronic measurement modules of the vehicle. The relay module is an electronic measurement module which sends its own measurements to the electronic control unit with the measurement messages received from the primary emitter module or modules.
Preferably, the method comprises a preliminary initialization step in order to define the role of each electronic measurement module of the vehicle, that is to say assign each module the function of primary emitter module, of secondary emitter module or of relay module.
According to one aspect of the invention, in this initialization step, each electronic measurement module emits, at different powers, an initialization message to the other electronic measurement modules and the electronic control unit in order to determine the distance, in terms of power, separating said module from the other modules and from the electronic control unit.
Each module which receives the initialization message emitted at a given power level then sends a response message comprising its identifier to the emitter module such that the emitter module then knows the power level at which it must emit to this module if this module has to receive measurement messages from it.
Advantageously, the electronic control unit receives, from each electronic measurement module, a list of the distances (in terms of power and not of physical distance) separating said module from the other modules and then compiles a message routing table.
More specifically, the electronic control unit classifies all the electronic measurement modules as a function of the determined distances (in terms of power) between the modules then determines the role of each module, that is to say whether each module is a primary emitter module (which must send its messages to at least one identified relay module), a relay module (which must receive measurement messages from one or more primary emitter modules and transfer them with its measurements to the electronic control unit) or a secondary emitter module (which must send its measurement messages directly to the electronic control unit).
The electronic control unit then informs each module of its role and in particular informs the primary emitter modules that they must emit at a power below the first threshold, the relay modules of the list of the identified primary emitter modules for which they must transfer the messages received to the electronic control unit in signals emitted at a power above the second threshold and, if necessary, the secondary emitter modules that they must emit signals comprising their measurement messages at a power above a third threshold.
Advantageously, the relay module concentrates the measurement messages received from a plurality of identified primary emitter modules from which it must receive messages before sending them grouped together to the electronic control unit with its own measurements.
The relay module can thus emit, at one and the same time, for example at high power, a set comprising the measurement messages received from the primary emitter modules and its own measurements, which makes it possible to ensure that all the messages sent by primary emitter modules and that the measurements performed by the relay module are received at one and the same time by the electronic control unit, thus avoiding the loss of any one of the messages. This also makes it possible to avoid a plurality of signal emissions at different instants, which strains the relay module and can therefore reduce the energy level stored in its battery.
Advantageously, the method comprises a step of sending of a switchover request to the electronic control unit following a switchover event to indicate to it that it is necessary to redefine all or some of the roles of the electronic measurement modules.
Such an event can be an energy level below a predetermined energy threshold. As a variant or in addition, the information on the battery level can be transmitted periodically to the electronic control unit such that the electronic control unit itself directly decides on the switchover.
The sending of a switchover request can be performed by any electronic measurement module whether it is a relay or emitter. The sending of a switchover request can also relate to any relevant specific type of event such as, for example, the detection of one or more new electronic measurement modules on the vehicle (for example replacing previous ones), the detection of one or more changes of positions or of location of the electronic measurement modules of the vehicle, the detection of a change of a measurement datum (for example the temperature in the tire or the load applied to the wheel). The sending of a switchover request can even be performed periodically (for example at the start of each running cycle, or every 24 hours, etc.).